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Low‐Overpotential Electrocatalytic Water Splitting with Noble‐Metal‐Free Nanoparticles Supported in a sp 3 N‐Rich Flexible COF
Author(s) -
Mullangi Dinesh,
Dhavale Vishal,
Shalini Sorout,
Nandi Shyamapada,
Collins Sean,
Woo Tom,
Kurungot Sreekumar,
Vaidhyanathan Ramanathan
Publication year - 2016
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201600110
Subject(s) - overpotential , tafel equation , materials science , noble metal , nanoparticle , nanocomposite , chemical engineering , covalent bond , water splitting , mesoporous material , covalent organic framework , metal , nanotechnology , catalysis , chemistry , composite material , electrochemistry , electrode , organic chemistry , porosity , photocatalysis , metallurgy , engineering
Covalent organic frameworks (COFs) are crystalline organic polymers with tunable structures. Here, a COF is prepared using building units with highly flexible tetrahedral sp 3 nitrogens. This flexibility gives rise to structural changes which generate mesopores capable of confining very small (<2 nm sized) non‐noble‐metal‐based nanoparticles (NPs). This nanocomposite shows exceptional activity toward the oxygen‐evolution reaction from alkaline water with an overpotential of 258 mV at a current density of 10 mA cm −2 . The overpotential observed in the COF‐nanoparticle system is the best in class, and is close to the current record of ≈200 mV for any noble‐metal‐free electrocatalytic water splitting system—the Fe–Co–Ni metal‐oxide‐film system. Also, it possesses outstanding kinetics (Tafel slope of 38.9 mV dec −1 ) for the reaction. The COF is able to stabilize such small‐sized NP in the absence of any capping agent because of the COF–Ni(OH) 2 interactions arising from the N‐rich backbone of the COF. Density‐functional‐theory modeling of the interaction between the hexagonal Ni(OH) 2 nanosheets and the COF shows that in the most favorable configuration the Ni(OH) 2 nanosheets are sandwiched between the sp 3 nitrogens of the adjacent COF layers and this can be crucial to maximizing their synergistic interactions.